This study aimed to evaluate the effects of Thymus capitatus and symbiotic (SynerAll®) supplementation in quail diets on growth, inner organ development, intestinal health, meat quality, and malondialdehyde (MDA) formation in breast meat. Seven-day-old equalized live weight of 160 healthy quail chicks randomly distributed into four dietary treatments with four replicates (10 chicks eachs). The treatment regimens were basal diet (T0), basal diet + 5 g kg-1T. capitatus (T1), basal diet + 10 g kg-1T. capitatus (T2), and basal diet + 2 g kg-1 symbiotic (T3). The feeding trial was conducted over 35 days. At 35 days of study by selecting 2 quails (1 male and 1 female) from each replicate were slaughtered and eviscerated. Body weight gain (BWG) was significantly improved in the T3 group compared with the other groups (p < 0.01). Feed intake (FI), feed conversion ratio (FCR), gut length, heart, proventriculus weights, cecal microbiota, meat color values, and pH did not change among the groups (p > 0.05). T. capitatus and symbiotic supplementation increased gizzard weight compared with the control group. Symbiotic supplementation (T3) increased liver and edible inner organ (EIO) weight compared with the control group (T0). Villi length in the T3 group was higher than that in the T0 and T1 groups in the ileum and was higher than that in the other groups in jejunum (p < 0.01). In addition, villi length in the T1 groups was higher from T0 groups in jejunum. Crypt depth increased in T1 group than in the T3 group in jejunum (p < 0.05) and T0 group’s crypt depth decreased than those of T1, T2 and T3 groups in ileum (p > 0.01). The villi length/crypt depth ratio increased in T3 group than those of T0, T1, and T2 groups in jejunum (p < 0.01) and T1 group’s ratio decreased from than in the T0 and T3 groups in ileum (p < 0.05). T. capitatus supplementation (T1 and T2) showed strong antioxidant activity and decreased malondialdehyde (MDA) levels in breast meat on the 3st and 5st days in the refrigerator at 4 ℃. It was concluded that symbiotic addition to quail diets can be used to increase performance and that T. capitatus supplementation can be used to suppress MDA formation and increase shelf life in meat.